The present invention relates to friction welding and in particular to the use of a shielding gas in the friction welding process.
Friction welding is used in the manufacture or repair of components such as integrally bladed rotor assemblies. Separately made blades are attached to the periphery of a disc or drum by their roots. The disc or drum is held stationary whilst the blades are reciprocated under pressure to develop the necessary weld temperature.
Friction welding is generally less susceptible to oxidation defects than conventional welding processes. The relative movement between the components prevents the ingress of ambient air into the weld and any oxides are transported away by the extruded material. Nevertheless defects have been discovered in the edge and corner regions of the weld, which could affect the integrity of the weld.
To prevent the formation of defects in the edge and corner regions of the weld it is known to use a shielding gas. French patent number 2 760 985 B1 discloses flowing a shielding gas through orifices in a nozzle to drive away oxygen. The nozzle is shaped to envelop the blade being welded onto a disc. A problem with this arrangement is that the nozzle extends into the weld area where space is restricted.
The present invention seeks to provide an improved method of friction welding in which a shielding gas envelops the weld area without the need for a shaped nozzle that extends into the weld area.
According to the present invention a method of friction welding workpieces together at an interface comprises the steps of holding a first workpiece in a fixed relationship to a second workpiece, oscillating the second workpiece with respect to the first workpiece, applying a load between the first and second workpieces so as to generate a temperature at the interface between the workpieces which is sufficient to weld the workpieces together, introducing opposing flows of a shielding gas on opposite sides of the interface to produce a continuous flow of shielding gas around the interface.
Preferably the opposing flows of shielding gas are introduced at an angle to the interface. The opposing flows of shielding gas are introduced through primary nozzles, which are spaced apart. The primary nozzles may be conical to diffuse the shielding gas and prevent turbulence. The primary nozzles introduce the shielding gas at a flow rate of the order of 40-150 liters/minute.
In a further embodiment of the present intention secondary nozzles are provided to direct a further flow of shielding gas towards the primary nozzles. The secondary nozzles introduce the shielding gas at a flow rate of the order of 25 liters/minute.
Preferably the shielding gas is an inert gas such as argon.
In the preferred embodiment of the present invention the first and second workpieces are preferably a disc and a blade of a rotor assembly.
A gas chamber may be created around the weld interface, which is partially sealed. In the preferred embodiment of the present invention the blades adjacent the weld interface define the partially sealed chamber.